Is it hard to learn to play the banjo?
Is banjo harder to learn than the guitar? Certainly not harder! Some things about the banjo could be considered easier; the strings are lighter gauge than a guitar and easier to push down. It does not take long to master a few simple things on both instruments.
Can you teach yourself banjo?
While there are a number of methods that you can use to teach yourself have to play the banjo, but you still need to listen well in order to get really good at it yourself. The best way to do that is to listen to banjo being played by professional banjo players.